The term prebiotic was first used in 1995 and can be defined as a non-digestible food ingredient that can deliver beneficial effects on health by selectively stimulating the growth and/or activity of specific health-promoting bacteria in the colon. In other words, prebiotics promote the growth of particular bacteria in the gut that are beneficial to intestinal health (for example Lactobacillus sp., Bifidobacteria sp. and Lactococcus sp.). They also inhibit the growth of bacteria that are potentially harmful to intestinal health (for example bacteria that produce toxins such as Clostridia and Escherichia coli). This is in contrast to probiotics, which are live bacteria capable of journeying through the gut into the large bowel. By helping increase the amount of ‘good’ bacteria, prebiotics are thought to promote a healthy environment in the intestine and so could potentially have health benefits.
The main types of prebiotics are fructo-oligosaccharides, e.g. inulin, and oligofructose and lacto-oligosaccharides, e.g. lactulose, galacto-oligosaccharides and lactosucrose. Foods naturally containing substances with prebiotic properties include leeks, chicory, asparagus, bananas, artichokes, garlic, onion, wheat, soybean and oats, and more recently some honeys have been suggested to have prebiotic properties. Sometimes foods with prebiotic properties are added to foods and are referred to as ‘functional foods’. Prebiotic-containing foods can be found in supermarkets and include, for example, some cheese products, yogurts and yogurt drinks, breakfast cereals and cereal bars.
Regular consumption of prebiotics has been suggested to have a wide range of potential health benefits including aiding mineral absorption (e.g. calcium), improving immune function, reducing blood cholesterol levels, playing a role in cancer prevention and helping to relieve constipation and irritable bowel syndrome. However, the strength of the evidence is stronger for some of these claims than others and further research in humans is required to determine whether some of these benefits exist when prebiotic-containing foods are consumed as part of a normal diet. To date, the most promising areas are calcium absorption and immune system effects.
There is a growing body of evidence demonstrating a positive effect of prebiotics on the intestinal flora in infants by increasing the number of ‘good’ bacteria in the gut. Accumulating research suggests that prebiotic infant formulas may help to alleviate conditions such as atopic dermatitis (allergic skin condition), constipation and also to reduce the risk of infection in early life.